Project Summary/ Abstract Sjgren's syndrome (SS) is an autoimmune disease in which exocrine tissue is damaged, resulting in loss of tears and saliva production. The diagnosis of SS is challenging and patients often experience symptoms for years before they are diagnosed. Once diagnosis is achieved, no SS-specific curative treatment options are available; rather treatments for SS are palliative. Thus, there is a critical need to identify etiologic events that will facilitate earlier diagnosis of SS and mitigate or abrogate the progression of this debilitating disease. Even though the immune system drives SS, few mechanistic studies of the seminal factors responsible for SS are reported. Studies in lupus, a related autoimmune disease, demonstrated that Myeloid Differentiation Factor Primary Response Protein 88 (MyD88) is critical for disease development. MyD88 is an adaptor molecule that is expressed ubiquitously and is required for most Toll-like receptor (TLR) signaling. Notably, TLRs are elevated locally (in salivary tissue) and in peripheral blood cells of SS patients, suggesting TLR signaling contributes to SS pathogenesis. Surprisingly, the role of MyD88 and TLR signaling has not been evaluated in depth in SS. Our central HYPOTHESES are that MyD88 expression in salivary tissue and in immune cells is crucial for SS initiation and progression and that TLR signals via MyD88 drive SS pathogenesis. Our OBJECTIVE is to evaluate the means by which MyD88-mediated signaling contributes to SS and to identify specific factors that activate TLR signaling pathways in SS. We will use a SS mouse model (NOD.B10) and our recently developed knockout strain of NOD.B10 mice that lack MyD88. These mice provide the opportunity to examine the role of MyD88 in SS. We will test our hypotheses through the following Specific Aims: (1) To determine whether MyD88 expression by hematopoietic cells is required for SS pathogenesis. These experiments will examine autoantibody production and salivary function to determine whether hematopoietic-intrinsic MyD88 expression is crucial for specific SS disease manifestations. (2) To evaluate the role of MyD88 in the generation and pathogenicity of autoantibodies in SS. These results will identify the role of MyD88 in the development of autoantibodies in SS, and will establish whether antibodies derived from MyD88-/- NOD.B10 mice have reduced pathogenicity in vivo. (3) To investigate the role of MyD88-dependent TLR2/4 activation in SS. We will determine whether signaling via TLR2/4 in salivary tissue contributes to SS in a MyD88-dependent manner. We will also overexpress a specific damage-associated molecular pattern that activates TLR2/4 in a MyD88-dependent manner to determine whether this accelerates SS. Finally, we will assess TLR2 and TLR4 blockade in SS to determine whether these attenuate disease. This study is innovative in that it will employ a novel mouse model to evaluate the role of MyD88, a key immune signaling molecule, in SS. The proposal is significant, as it will provide new knowledge regarding the role of MyD88 and TLR2/4 signaling in SS initiation and progression. This work will lay the foundation for future studies to identify therapeutics for patients with SS and other autoimmune diseases that target TLR/MyD88-related pathways.